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What does exhaust resonator do?

I'm trying to lower my EGTs. I get conflicting opinions on just removing the muffler or removing muffler and resonator. Talking to friends I get different answers on purpose of resonator.

Also is it a big contributor to back pressure?

One friend said just cutting out the mufler will accomplish about 75% of what I want to achive. . Bases this on fact I have a 3 inch exhaust brake (which I don't want to replace) so going to 4 inch exhaust pipe won't help all that much as compared to just removing muffler.

Yank out your mufler but leave the resonator in place!! I took both out and the drone was horrendous. I ended up putting another resonator (from pay it foreward) back in a few weeks later and it sounded great outside without the drone in the cab. The resonator is straight through so there shouldn't be hardly any change in backpressure with it.

Depening on where you locate the resinator, depends on what sounds you will get. I have a 40 inch long Donaldson Full Flow Muffler on mine that RIP installed when we put on the 4 inch exhaust system. With the Resinator tip installed, the exhaust tone sounds more mellow/deep than with just a straight tip.

The best way to find out is to try several different resinators and sets up in the pipe if you can before you buy.

I got my exhaust system from Source Automotive and when I was trying to decide, Rip would put up varied tips and you could hear the tone change on the fly while the truck was idling.

More specific to your question the "Resonator" is really misnamed. IMO it should be labeled something more like "De-Resonator" because that is its purpose.

A background in resonance. Resonance is basically the effect of multiplying vibration. Typically it will occur at specific frequencies for any given piece of machinery. A good example of this is a musical chord. Press the the right 3 keys on a piano simultaneously. You can hear all 3 tones distinctly, but you also hear a 4th different tone. Another example would be shaft bearing vibration. If you rotate the shaft at xxx RPM the vibration is low, rotate it at yyy RPM and you will destroy the bearing.

In the case of the cummins exhaust, it relates to sound. Sound is a vibration.

To illustration what I mean, I am sure at one time or another everyone has tried to play a trombone (trumpet etc). The vibration source is your lips in the mouth piece. Any one can try to play, but unless you get the vibration of your lips right in conjunction with the right amount of air flowing through the horn all that comes out is a squawk. When you get it right, the sound booms out the other end. That is resonance, or very close to it. In the case of a trombone, move the slide in or out and change the buzzing frequency of your lips and do it well enough you get a chair at the Boston Pops Orchestra otherwise just pack your lunch and go to work as ussual.

Now for further musical relation. Many times, especially non OEM, a diesel exhaust pipe is almost nothing more than a big trombone. The point that resonance is achieved really is base upon the configuration of the equipment. It is engine RPM which causes exhaust gas pulses at a certain frequency, exhaust gas flow speed, size of the exhaust pipe and length of the exhaust pipe etc etc etc. . . . . If the right conditions occur so does resonance and the sound booms.

So the purpose of the "resonator" is to prevent resonance from happening. Specically, the resonator does this by momentarily storing exhaust pressure in the exhaust pipe. This occurs when a pressure pulse moves down the pipe. During the lull period before the next pressure pulse this pressure gets released rapidly. Effectively, it creates a "counter" pressure pulse that messes with pulse frequency of the pipe and hopefully prevents resonance.

Jim, way more than I wanted to know!!! But thanks, I actually knew a lot of this, I did vibration analysis on rotating equipment in power plants for a few years. I received very conflicting information from diesel mechanics and Dodge. I originally assumed it was tuned to reduce "noise" but Dodge mechanic confused me. I'll just think of it as a mini muffler and leave it in but take out real muffler.

Jim, way more than I wanted to know!!! But thanks, I actually knew a lot of this, I did vibration analysis on rotating equipment in power plants for a few years. I received very conflicting information from diesel mechanics and Dodge. I originally assumed it was tuned to reduce "noise" but Dodge mechanic confused me. I'll just think of it as a mini muffler and leave it in but take out real muffler.

THanks for the replies.

LOL Figures. . . .

Yes, as Forrest says, it is basically a little muffler. But it is placed at a specific point in the exhaust pipe to "de-resonate" the exhaust note. Thats why the OEM exhaust comes with a resonator and an a muffler. And thats why is is not called "the little muffler".

I believe the resonator is the only spot in the OEM exhaust that uses a small section of 4 inch pipe other than the tip.